Power over Ethernet (PoE) refers to delivery of power from power sourcing equipment (PSE) to powered devices (PDs) through Ethernet cabling. IEEE 802.3af and 802.at are standards which provide specific implementation details for such power delivery.
Examples of PSE include network switches and hubs. Examples of PDs include wireless access points, IP phones, and IP cameras.
Presently, there is no enforcement over how the PSE delivers power over the four twisted-wire pairs of an Ethernet cable (e.g., Cat 5, Cat 5e, Cat 6, etc.). Accordingly, it is currently possible for the PSE to deliver power to a PD over twisted-wire pairs of the cabling that do not carry data between the PSE and the PD. For example, through an Ethernet cable, it is possible for the PSE to exchange data with a PD only through first and second wire pairs of the Ethernet cable (e.g., 100 Mbps), and to deliver power only through the other twisted pairs, i.e., the remaining third and fourth twisted pairs of the Ethernet cable. It is also currently possible for the PSE to exchange data with a PD only through first and second twisted pairs of the Ethernet cable, and to deliver power through all of the twisted pairs of the Ethernet cable, i.e., power delivery to the PD using all four twisted pairs.